Redox-Neutral Manganese(I)-Catalyzed C-H Activation: Traceless Directing Group Enabled Regioselective Annulation

A strategy is reported in which traceless directing groups (TDGs) are used to promote the redox-neutral Mn-I-catalyzed regioselective synthesis of N-heterocycles. Alkyne coupling partners bearing a traceless directing group, which serves as both the chelator and internal oxidant, were used to control the regioselectivity of the annulation reactions. This operationally simple approach is highly effective with previously challenging unsymmetrical alkyne systems, including unbiased dialkyl alkynes, with perfect regioselectivity. The simple conditions and the ability to carry out synthesis on a gram scale underscore the usefulness of this method. The application of this strategy in the concise synthesis of the bioactive compound PK11209 and the pharmaceutical moxaverine is also described.